This invention relates to polyurethane-type adhesives and their use in the bonding of substrates.
Polyurethane adhesives constitute a broad class of polymeric materials having a wide range of physical characteristics. These polymers are produced by the reaction of a polyisocyanate with a polyfunctional compound having active hydrogens in its structure. This active hydrogen compound is generally a liquid or solid capable of being melted at relatively low temperatures. Most commonly, the active hydrogen compound contains hydroxyl groups as the moieties having the active hydrogen and thus are termed polyols, e.g., the polyols of polyesters, polyester amides, or poly-ethers, or mixtures of two or more such materials. For reasons of commercial availability and cost, the polyols most commonly employed in the preparation of polyurethane adhesives are the poly-ethers having hydroxyl terminated chains and hydroxyl terminated polyesters.
Although a wide variety of physical and chemical properties are obtainable by the proper selection of a polyisocyanate and the polyol as well as the conditions under which the polyurethane reaction is carried out, the resulting polyurethane adhesives often do not adhere well to various substrates, e.g., vinyl polymers and the like, and often exhibit poor lap shear strength and poor impact strength.
Accordingly, it is highly desirable to provide a polyurethane adhesive exhibiting increased lap shear strength and/or impact strength.